Projector with foreign matter detecting means

ABSTRACT

A projector has an image generating device for generating an image, and a housing, having the image generating device disposed therein and having an opening defined therein for emitting therethrough projection light representing the image from the image generating device. A projection mirror is mounted on an outer surface of the housing for reflecting the projection light to project the image onto a projection surface. An optical system is disposed in the opening for applying the projection light to the projection mirror. The projector also has a foreign matter detector for detecting foreign matter which enters a light path of the projection light between the optical system and the projection mirror.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector having a projection mirrorfor reflecting projection image light generated by an image generatingdevice to project an enlarged image onto a projection surface such as anexternal screen or the like, and more particularly to a projector whichis designed for higher luminance and has a foreign matter detectingmeans.

2. Description of the Related Art

Projectors for projecting an enlarged view of image light generated byan image generating device onto a projection surface such as an externalscreen or the like are used in various applications. In recent years,efforts have been made to increase the luminance of images projected byprojectors, and, as a result, more and more projectors project highlyintensive light to form bright images. Accordingly, such projectors haveprojection lens that are heated to very high temperatures.

Recently, there has been disclosed a projector having a housing fromwhich projection light is emitted through an opening defined in thehousing, and a projection mirror for reflecting the projection light toproject an image onto a projection surface.

As shown in FIG. 1 of a schematic side elevational view, projector 50has housing 51 with opening 52 defined therein. Opening lens 53 forprojecting projection light is disposed in opening 52. Housing 51supports thereon projection mirror 54 disposed in confronting relationto opening lens 53. When projector 50 is in use, projection image light55 generated by an image generating device is emitted through openinglens 53 from opening 52, and reflected by projection mirror 54 toproject an enlarged image onto an external screen (not shown). A lightsource, the image generating device, and an optical system of projector50 are omitted from illustration. Projection mirror 54 may also be usedas a lid for opening 52, and may be turned down to close opening 52 whenprojector 50 is not in use.

Japanese laid-open patent publication No. 11-119343 discloses aprojection-mirror-type projector as shown in FIGS. 2A and 2B of theaccompanying drawings. The disclosed projector comprises light source64, liquid crystal display device 65, projection mirror 63 forprojecting projection light modulated by an image which is displayed byliquid crystal display device 65 onto an external screen or the like, apair of reflection mirrors 66, 67 for reflecting the projection lightfrom liquid crystal display device 65 toward projection mirror 63, andhousing 61 which accommodates therein the projection optical systemincluding light source 64, liquid crystal display device 65, andreflection mirrors 63, 66, 67.

Housing 61 has opening 62 provided therein between liquid crystaldisplay device 65 in housing 61 and projection mirror 63, for emittingthe projection light from liquid crystal display device 65 towardprojection mirror 63. Projection mirror 63 is angularly movably mountedon housing 61 for selectively opening or closing opening 62. Projectionmirror 63 serves as part of the projection optical system when it opensopening 62, and serves as a lid for opening 62 when it closes opening62.

As described above, with the projector having the projection mirror, theopening lens and the reflection mirrors which are heated to a relativelyhigh temperature are exposed out of the housing. Furthermore, whenforeign matter such as a user's finger, an object in the room, or dustparticles enters the opening, a sharp temperature rise occurs becausethe projection light directed toward the projection mirror is blocked bythe foreign matter. Since such a sharp temperature rise may possiblycause a burn on the user or a fire in worst cases, some countermeasuresneed to be combined with the projector.

For example, in case a detecting circuit with a sensor assembly forsimply detecting foreign matter that enters the opening is added, hugequantities of sensors are needed. In case the sensor assembly generallydetects foreign matter in a wide range of space, there needs a pluralityof sensors. Furthermore, as the size of foreign matter to be detected issmaller, the sensor assembly requires an increased number of sensors,and hence the detecting circuit becomes larger in circuit scale.

If the projection-mirror-type projector disclosed in Japanese laid-openpatent publication No. 11-119343 is designed for higher luminance, thenthe intensity of the projection light in the vicinity of the reflectionmirrors is increased, resulting in a higher temperature at thosereflection mirrors. However, there is nothing disclosed in Japaneselaid-open patent publication No. 11-119343 about countermeasures againstforeign matter which may possibly find its way into the path of theprojection light.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a projector which isof a relatively simple structure and is capable of efficiently detectingforeign matter, even if it is small in size, in a relatively large rangeof space.

To achieve the above object, a projector according to the presentinvention has an image generating device for generating an image, ahousing, the image generating device being disposed in the housing, thehousing having an opening defined therein for emitting therethroughprojection light representing the image from the image generatingdevice, a projection mirror mounted on an outer surface of the housingfor reflecting the projection light to project the image onto aprojection surface, optical means disposed in the opening for applyingthe projection light from the image generating device to the projectionmirror, and foreign matter detecting means for detecting foreign matterwhich enters a light path of the projection light between the opticalmeans and the projection mirror.

The foreign matter detecting means comprises a light-emitting elementfor emitting foreign matter detection light for detecting foreign matteracross the light path of the projection light, a plurality of detectionmirrors for reflecting the detection light across the light path of theprojection light, a light-detecting element for detecting the detectionlight which has been reflected by the detection mirrors, and an electriccircuit for controlling the projector in response to an output signal,representing the detected foreign matter detection light, from thelight-detecting element.

The light-emitting element comprises a semiconductor light-emittingdevice such as a semiconductor laser, a light-emitting diode (LED), orthe like, for emitting the detection light which has a wavelengthdifferent from the wavelength of the projection light. Thelight-detecting element comprises a semiconductor light-detecting devicesuch as a photodiode or the like.

The detection mirrors of the foreign matter detecting means comprise twodetection mirrors which are disposed in confronting relation to eachother across the light path of the projection light, for reflecting thedetection light in multiple paths therebetween. Alternatively, aplurality of the detection mirrors are disposed in confronting relationto each other across the light path of the projection light, forreflecting the detection light successively therebetween.

The electric circuit comprises a detecting circuit for detecting whetherthe detection light is detected or not in response to the output signalfrom the light-detecting element, a lamp control circuit for turning onand off a light source lamp which emits the projection light, inresponse to an output signal from the detecting circuit, a timer circuitfor monitoring the output signal from the detecting circuit for apredetermined period of time to determine whether the projector is in adangerous situation or not, and a power supply control circuit forturning on and off a power supply of the projector in response to thedetermination made by the timer circuit.

As described above, according to the projector of the present invention,the foreign matter detecting means is disposed in a region near theoptical means where the projection light emitted from the opening in thehousing is highly intensive, and detects the entry of foreign matter tokeep the region near the optical means in safety. When the foreignmatter detecting means detects foreign matter that enters the light pathof the projection light, the light source lamp is turned off and thepower supply is turned off for safety. The light-emitting element of theforeign matter detecting means is arranged so as not to spread the beamof the detection light or so as to give some directivity to the beam ofthe detection light. The detection mirrors for reflecting the detectionlight from the light-emitting element is disposed between thelight-emitting element and the light-detecting element to guide thedetection light to the light-detecting element, so that the blocking ofthe detection light by foreign matter can be detected. Thelight-emitting element and the light-detecting element which areprovided in a pair are easily capable of detecting small foreign matterthat has entered the light path in a relatively large range of spacewith a minimum circuit scale.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a conventionalprojection-mirror-type projector;

FIG. 2A is a plan view of another conventional projection-mirror-typeprojector;

FIG. 2B is a side elevational view of the conventionalprojection-mirror-type projector shown in FIG. 2A;

FIG. 3 is a perspective view of a projector according to a firstembodiment of the present invention;

FIG. 4 is a side elevational view of the projector according to thefirst embodiment of the present invention;

FIG. 5 is a plan view of a foreign matter detector of the projectoraccording to the first embodiment of the present invention;

FIG. 6 is a block diagram of the foreign matter detector;

FIG. 7 is a plan view of a foreign matter detector of a projectoraccording to a second embodiment of the present invention;

FIG. 8A is a plan view of a projector according to a third embodiment ofthe present invention; and

FIG. 8B is a side elevational view of the projector according to thethird embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows in perspective a projector according to a first embodimentof the present invention, and FIG. 4 shows in side elevation theprojector according to the first embodiment of the present invention.

As shown in FIGS. 3, projector 1 comprises housing 2 having opening 3for emitting therethrough projection light to project an image onto aprojection surface. Opening lens 4 is disposed in opening 3 andprojection mirror 5 is mounted in confronting relation to opening lens4. The interior of opening 3 is sealed to prevent dust particles andother foreign matter from entering through opening 3 into housing 2.

As shown in FIG. 4, projector 1 also comprises an optical systemdisposed in housing 2. The optical system includes light source lamp 21for emitting projection light, image generating device 22 for generatingan image, and reflection mirrors 23, 24 for guiding the projection lightto opening lens 4. Image generating device 22 comprises, for example, aliquid crystal display device, a DMD (Digital Micromirror Device), orthe like. Although not shown, projection mirror 5 may be disposed on alid that is capable of closing opening 3 in housing 2, and whenprojector 1 is not in use, opening 3 may be closed by the lid.

Image projection light 6 generated by image generating device 22 isemitted through opening lens 4 and applied to projection mirror 5, whichreflects image projection light 6 and projects an enlarged image thereofonto external screen 11.

On the light path between image generating device 22 and opening lens 4,image projection light 6 has its light beam substantially not spread,i.e., not diverged. Therefore, image projection light 6 that is emittedfrom opening lens 4 toward projection mirror 5 has such a very highintensity that the air in the light path of image projection light 6 isheated to a high temperature. Furthermore, when foreign matter such as auser's finger, an object in the room where the projector is installed,or dust particles blocks image projection light 6, a sharp temperaturerise occurs and tends to cause dangerous situations. If the temperatureof the region where the image projection light is emitted is to belowered, then the image projection light may be spread into a light spotgreater than image generating device 22. However, such a solution wouldnot be preferable because it would require the opening and the housingto be increased in size.

According to the present embodiment, foreign matter detector 26 isdisposed between opening lens 4 and projection mirror 5 in a range to bedetected of the light path of image projection light 6 for preventingdangerous situations from being developed which would tend to occur whenforeign matter enters the light path that is kept at a relatively hightemperature between opening lens 4 and projection mirror 5.

FIG. 5 shows in plan structural details of foreign matter detector 26.As shown in FIG. 5, foreign matter detector 26 comprises light-emittingelement 8 for emitting detection light 12, a plurality of detectionmirrors 9 for reflecting detection light 12 emitted from light-emittingelement 8, and light-detecting element 10 for detecting detection light12 reflected by detection mirrors 9.

Housing 2 has a pair of confronting side walls 7 on the sides of opening3. Light-emitting element 8, detection mirrors 9, and light-detectingelement 10 are mounted on the confronting surfaces of side walls 7.Detection light 12 emitted from light-emitting element 8 travelstransversely across the light path of image projection light 6 betweenopening lens 4 and projection mirror 5. Detection light 12 is thenreflected a plurality of times efficiently by detection mirrors 9, andaccurately detected by light-detecting element 10.

Light-emitting element 8 comprises a semiconductor light-emitting devicesuch as a semiconductor laser for emitting infrared rays, alight-emitting diode (LED), or the like, and is arranged so as not tospread the beam of emitted detection light 12 or so as to give somedirectivity to the beam of emitted detection light 12. Light-detectingelement 10 comprises a semiconductor photo-detecting device such as aphototransistor, a photodiode, or the like. Detection mirrors 9 aredisposed in mutually confronting positions. Detection light 12 emittedfrom light-emitting element 8 is reflected by the reflecting surfaces ofdetection mirrors 9, and reliably applied to light-detecting element 10.If required, each of detection mirrors 9 has an angle adjusting functionto adjust the angle of tilt of the reflecting surface thereof. Foreignmatter detector 26 itself may have an angle adjusting function. In FIGS.3 and 5, two detection mirrors 9 are shown as being disposed inconfronting relation to each other. However, the number of detectionmirrors may be increased if necessary.

The wavelength of detection light used by foreign matter detector 26should preferably be selected so as to be different from the wavelengthsof image projection light 6 emitted to display images, i.e., so as to bedifferent from the wavelengths of visible light rays. Detection mirrors9 should preferably be provided for exclusive use in detection offoreign matter. Since such dedicated detection mirrors 9 can bepositioned so as not to reflect the image projection light, the contrastof projected images is prevented from being lowered.

FIG. 6 shows in block form foreign matter detector 26 according to thefirst embodiment. As shown in FIG. 6, foreign matter detector 26 haselectric circuit 18 for processing a signal that is generated whenforeign matter enters the light path of image projection light 6. Ifforeign matter detector 26 detects that the detection light 12 isblocked by foreign matter that enters the light path, then foreignmatter detector 26 turns off light source lamp 21. If foreign matterdetector 26 detects that the detection of foreign matter does no longerexist, then foreign matter detector 26 turns on light source lamp 21again to emit image projection light. If foreign matter detector 26detects the elapse of a period of time for which foreign matter has beendetected as being dangerous, then foreign matter detector 26 turns offthe power supply of projector 1.

Electric circuit 18 of foreign matter detector 26 comprises detectingcircuit 13 for detecting whether the detection light 12 is detected ornot in response to output signal from light-detecting element 10, lampcontrol circuit 14 for turning on or off light source lamp 21 inresponse to an output signal from detecting circuit 13, timer circuit 15for monitoring the output signal from detecting circuit 13 for a certainperiod of time to determine whether there has been developed a dangeroussituation or not, and power supply control circuit 16 for turning on oroff the power supply In response to the determination made by timercircuit 15.

In electric circuit 18, as a result of the detection by light-detectingelement 10 an output signal is supplied to detecting circuit 13, whichdetermines whether the detection light 12 is detected or not in responseto an H/L output level of the output signal. For example, if thedetection light 12 is detected indicating that projector 1 is normal,then detecting circuit 13 outputs an H-level output signal. If the pathof the detection light 12 is blocked and hence the detection light 12 isnot detected indicating that projector 1 is abnormal, then detectingcircuit 13 outputs an L-level output signal representing that foreignmatter has entered the light path between opening lens 4 and projectionmirror 5.

If detecting circuit 13 determines that the detection light 12 is notdetected, then lamp control circuit 14 judges that projector 1 is in adangerous situation, and de-energizes light source lamp 21. Lamp controlcircuit 14 forcibly turns off a lamp energization control device tode-energize light source lamp 21. Specifically, lamp control circuit 14changes the voltage of the lamp energization control device with aswitching device such as a transistor to de-energize light source lamp21. If the foreign matter is removed and the detection light 12 isdetected again, lamp control circuit 14 energizes light source lamp 21again to resume the emission of the image projection light.

Rather than de-energizing light source lamp 21, an image output may becut off. When an image output is cut off, projector 1 displays anall-black image, i.e., emits no image projection light from opening lens4. Therefore, the light path between opening lens 4 and projectionmirror 5 is reliably prevented from being heated to a high temperature.For example, an image switcher or OSD (On-Screen Display) switcher, animage output unit, or an IC (Integrated Circuit) may be controlled tointercept images. If images are intercepted at a stage prior to the OSDswitcher, then an OSD message such as an error message can be displayed.

Timer circuit 15 monitors checking several times the H/L output levelfrom detecting circuit 13, indicating whether detection light 12 isdetected 15 or not, at intervals of several seconds on a software basis.For example, timer circuit 15 employs a counter of a timer circuitfunction built in a CPU (Central Processing Unit), and confirms one timethe voltage level indicating that no detection light 12 is detected,every second. If timer circuit 15 finds the L output level to beconstant for 10 seconds, then timer circuit 15 judges that foreignmatter is present in the light path and projector 1 is in a dangeroussituation. The period of time for which timer circuit 15 monitors theoutput level from detecting circuit 13 may be set to any desired lengthof time of timer circuit 15.

Power supply control circuit 16 turns off the power supply in responseto the determination of a dangerous situation by timer circuit 15. Powersupply control circuit 16 has a switching device such as a transistor,for example, for switching the ON control terminal voltage of the powersupply to turn on or off the power supply. Alternatively, power supplycontrol circuit 16 turns on or off the power supply with an IC on asoftware basis.

After power supply control circuit 16 has turned off the power supply,and when the power supply is turned on again, if the detection offoreign matter by foreign matter detector 26 has not yet been canceled,then power supply control circuit 16 interrupts the turning-on of thepower supply. When foreign matter is detected, power supply controlcircuit 16 warns the user by displaying an error such as a foreignmatter failure by light-emitting diodes, a display panel, or the like.After power supply control circuit 16 has turned off the power supply,and when the power supply is turned on again, if the detection offoreign matter by foreign matter detector 26 has been canceled, thenpower supply control circuit 16 turns on the power supply.

In case an image output is shut off rather than turning off light sourcelamp 21, then an error message is displayed as a warning by the OSD. Incase an image output is shut off upon detection of foreign matter, thenonly the original image signal is shut off at a stage prior to the OSDswitcher. Since projector 1 displays an all-black image and can displayonly an OSD image, an error message can be displayed on the screen forthe user to confirm the error. The error message is preferably of a sizethat is so small as not to make the projection light hot, e.g., of asize that is not greater than 1/10of the projected image size, and is ofa brightness that is so small as not to make the projection light hot,e.g., of a brightness achieved by displaying a dark color such as grayor the like rather than white.

According to the first embodiment, since the single detecting circuit iscapable of detecting whether foreign matter is present in the light pathor not, projector 1 is made up of a minimum number of parts and ishighly efficient. Projector 1 thus has a reduced number of parts,consumes a reduced current, and can be manufactured at a reduced cost.Projector 1 can also be used in safety even if it is desired for higherluminance because it has detecting circuit 13 for preventing a sharptemperature rise due to foreign matter.

FIG. 7 shows in plan a foreign matter detector of a projector accordingto a second embodiment of the present invention. The number of detectionmirrors for reflecting detection light emitted from the light-emittingelement is selected depending on a range of space where to detectforeign matter and the size of foreign matter to be detected. If thenumber of times that the detection light is reflected is to beincreased, then the number of detection mirrors may be increased.According to the second embodiment, however, as shown in FIG. 7, tworelatively large detection mirrors 19 are disposed in confrontingrelation to each other across the light path, such that detection light12 is reflected at a plurality of points on each of detection mirrors19. According to the second embodiment, a range of space where to detectforeign matter can be established as desired by changing the size of thedetection mirrors and the number of times that the detection light isreflected thereby. By reducing spaces between the light beams reflectedby each detection mirror, the foreign matter detector can detectrelatively small foreign matter. The spaces between the light beamsreflected by each detection mirror can be selected as desired dependingon the size of foreign matter to be detected.

FIG. 8A shows in plan a projector according to a third embodiment of thepresent invention, and FIG. 8B shows in side elevation the projectoraccording to the third embodiment of the present invention. Theprojector according to the third embodiment has a reflection mirror 38for reflecting image projection light to the projection mirror, insteadof opening lens 4 described above.

As shown in FIGS. 8A and 8B, the projector comprises housing 32 havingopening 33 for emitting therethrough projection light. An inner wall ofopening 33 has emission port 34 for emitting therethrough imageprojection light from image generating device 22. Protective lens 35through which the image projection light from image generating device 22passes is disposed in emission port 34. The interior of opening 33 issealed and emission port 34 is closed by protective lens 35 forpreventing dust particles from entering through opening 33 into housing32.

Image projection light from image generating device 22 is reflected byreflection mirror 37, passes through protective lens 35 in emission port34, and is applied to reflection mirror 38. The image projection lightthat is applied to reflection mirror 38 is reflected thereby and appliedto projection mirror 39, which reflects the image projection light toproject an image represented thereby onto a projection surface.

As in the projectors according to the first and second embodiments, theprojector according to the third embodiment has foreign matter detector40 for detecting foreign matter which enters the light path of the imageprojection light between reflection mirror 38 and projection mirror 39.Details of foreign matter detector 40 will not be described below as itis identical in structure to foreign matter detector 26 of projector 1according to the first embodiment.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

1. A projector comprising: an image generating device for generating animage; a housing having said image generating device disposed thereinand having an opening defined therein for emitting therethroughprojection light representing the image from said image generatingdevice; a projection mirror mounted on said housing, the projectionmirror being positioned to reflect said projection light onto aprojection surface; an optical element disposed in said opening so as totransmit said projection light to said projection mirror; and a foreignmatter detector arranged so as to detect a presence of foreign matterlocated in a light path of the projection light between said opticalelement and said projection mirror. 2-20. (canceled)
 21. A projectorhaving an image generating device, comprising: a housing having anopening; and a foreign matter detector including: a light-emitter toemit detection light; a light detector to detect said detection light;and a controller to control the projector based on a signal from saidlight detector, wherein projection light representing an image on theimage generating device goes through said opening, and wherein at leastpart of said detection light travels transversely across the light pathof said projection light.
 22. The projector according to claim 21,further comprising: a mirror to reflect said detection light.
 23. Theprojector according to claim 21, further comprising: a plurality ofmirrors to reflect said detection light, wherein said plurality ofmirrors are disposed in a mutually confronting position across saidprojection light that goes through said opening.
 24. The projectoraccording to claim 23, wherein at least one of said plurality of mirrorsreflects said detection light twice or more.
 25. The projector accordingto claim 21, further comprising: exactly two mirrors to reflect saiddetection light, wherein said detection light is reflected in multiplepaths between said two mirrors.
 26. The projector according to claim 21,further comprising: a projection mirror mounted outside of said housing,wherein said detection light is reflected by said projection mirrorafter going through said opening.
 27. The projector according to claim26, wherein said projection mirror is angularly movably mounted toselectively open or close said opening, and wherein said projectionmirror serves as part of a projection optical system when opening saidopening and serves as a lid when closing said opening.
 28. The projectoraccording to claim 21, wherein a peak wavelength of said detection lightis in the infrared region.
 29. The projector according to claim 21,wherein said controller de-energizes a light source when said signalfrom said light detector indicates no-detection of said detection lightfor a predetermined period.
 30. The projector according to claim 29,wherein said controller energizes said light source when said signalfrom said light detector indicates detection of said detection light.31. The projector according to claim 21, wherein said controller cutsoff said image when said signal from said light detector indicatesno-detection of said detection light for a predetermined period.
 32. Theprojector according to claim 31, wherein said controller displays an OSD(On-Screen Display) when said controller cuts off said image.
 33. Theprojector according to claim 32, wherein at least part of said OSD isgray.
 34. The projector according to claim 31, wherein a peak wavelengthof said detection light is different from the wavelength region of saidprojection light.
 35. The projector according to claim 39, wherein saidpredetermined period is arbitrary.
 36. The projector according to claim31, wherein said predetermined period is arbitrary.
 37. The projector ofclaim 1, wherein, said foreign matter detector comprises: a lightemitter positioned so as to emit detection light across said light pathof the projection light; a plurality of detection mirrors positioned soas to reflect said detection light across said light path of theprojection light; a light-detecting element positioned so as to receivesaid detection light which has been reflected by said detection mirrors;and an electric projector control circuit connected to receive an outputsignal generated by the light-detecting element, and wherein saiddetection mirrors are mounted on opposing side walls of the opening andacross said light path of the projection light.
 38. The projectoraccording to claim 21, further comprising: a plurality of detectionmirrors to reflect said detection light, wherein said detection mirrorsare mounted on opposing side walls of the opening.
 39. The projectoraccording to claim 21, further comprising: exactly two detection mirrorsto reflect said detection light, wherein said one of said two detectionmirrors is mounted on each of opposing side walls of the opening, andwherein said detection light is reflected in multiple paths between saidtwo detection mirrors.